Skip to content

README.md

Latest commit

 

History

History
46 lines (33 loc) · 1.84 KB

README.md

File metadata and controls

46 lines (33 loc) · 1.84 KB

CNC-Router-Handwheel

This repo contains the firmware for an ESP32 based CNC router handwheel to be used with Candle2

Important Note

Candle2 communicates with the pendant at 230400 baud. There is an issue in the ESP32 core in file packages\esp32\hardware\esp32\3.3.8\cores\esp32\esp32-hal-uart.c (as of 3.3.8). UART uses REF_TCIK (1MHz) as clock for baud rates under a certain limit and the APB clock (80MHz) UART_SCLK_APB over that limit. This is controlled via a define REF_TICK_BAUDRATE_LIMIT with default value 250000. However, I noticed corruption and garbled characters at 230400 baud using the REF_TCIK clock, which go away when switching to the APB clock by changing the REF_TICK_BAUDRATE_LIMIT to 200000:

#define REF_TICK_BAUDRATE_LIMIT 200000  // this is maximum UART badrate using REF_TICK as clock

This is likely because at 1MHz, REF_TICK cannot generate baud 230400 with low error:

1,000,000 / 230,400 ≈ 4.340

The UART divider must be integer or fractional with limited resolution. The actual achievable rate ends up being off by ~3–4%, which is way outside the safe UART tolerance (typically <2%).

Using APB:

80,000,000 / 230,400 ≈ 347.22

The UART fractional divider can represent this with very low error (typically <0.1%).

Unfortunately, this is a hard define and cannot be overriden via a compiler directive, so we must sadly edit the core file and unfortunately, this patch needs to be applied every time the core is upgraded :(

The long term fix is to implement this code:

#include "driver/uart.h"
#include "hal/uart_ll.h"
#include "soc/uart_reg.h"
#include "soc/uart_struct.h"

void forceUart0ApbClock(uint32_t speed)
{
    uart_ll_set_sclk(UART_LL_GET_HW(0), SOC_MOD_CLK_APB);
    uart_set_baudrate(UART_NUM_0, speed);
}

and call after Serial has started with Serial.Begin().